含逆变型分布式电源的配电网正序综合阻抗纵联保护

为解决逆变器控制策略对含逆变型分布式电源的配电网的故障特性的影响问题,提出了一种基于正序分量综合阻抗的纵联保护新原理。该原理利用线路两端正序电压相量之差与线路两端正序电流相量之和的比值构成正序分量综合阻抗。区内与区外发生故障时,正序分量综合阻抗的幅值变化明显,据此可以区分线路上的内部和外部故障。新原理特征量明显,容易整定,不受分布式电源控制策略的影响,抗过渡电阻能力强。PSCAD仿真验证了该原理的有效性。     

基于比例积分谐振的微网逆变器电压均衡控制策略研究

对于工作在离网模式下的微网逆变器,在可能会出现的负载不对称或者单相负载运行场合,采用传统的电压电流双闭环控制方法会导致输出电压严重不平衡,从而危害供电设备以及整个系统。基于分裂电容式的三相四线逆变器系统,针对逆变器在离网模式下带不平衡负载运行的问题,建立相关数学模型分析抑制不平衡问题,分析传统比例积分控制的缺陷,并在此基础上采用正负序分离独立控制和比例积分准谐振控制策略。同时针对微电网运行状态平滑切换的要求,给出一种基于间接电流控制策略的平滑切换控制策略。仿真结果证明该控制策略的正确性。最后在微电网逆变器实验平台上通过实验验证了该方案的实用性和可行性。     

交直流混合微电网TNPC变换器的死区电压矢量偏差及修正

对T型中点箝位型双向变换器在矢量空间中的死区电压矢量偏差进行分析,总结其发生规律,并根据参考电压矢量的位置和幅值得到提前修正的指令电压矢量。从线性调制空间到过调制空间得到相应的伏秒特性方程的调整办法。同时,考虑到系统在动态扰动下可能引发的欠补偿或过补偿,引入一个补偿深度的调节因子,实现脉宽调制(PWM)指令电压矢量的自适应修正。该方法可推广到有更多电平的变换器中,避免了采用传统PWM脉冲宽度整形法时出现的脉冲损失或饱和问题。     

小直径深孔冷板流道枪钻加工工艺参数研究

小直径深孔冷板流道的加工精度直接影响深孔冷板的散热效率和使用寿命.文中采用正交实验法对深孔流道的枪钻加工工艺进行了研究,通过分析刀具转速、进给量及冷却液流量对深孔流道中心线偏差的影响规律,优化了工艺参数.试验结果表明,小直径深孔冷板流道中心线偏斜≤0.9 mm/m,可满足深孔冷板的精度要求.     

联轴节的精密找正

分析了联轴节偏差的形式，给出了一种规范的联轴节精密找正的方法。     

保偏光子晶体光纤图像特征孔中心提取算法

保偏光子晶体光纤快慢轴的检测是保偏光子晶体光纤应用的关键技术。针对保偏光子晶体光纤端面空气孔数量多、尺寸存在差异及噪声和伪边缘干扰圆心定位精度的问题,提出一种双峰均值二值化法粗定位和径向扫描三点法精定位相结合的方法。采用双峰均值二值化法实现空气孔重心的粗定位;利用大空气孔定方位,选取两个具有结构对称的空气孔区域,去除粗大误差点,径向扫描法确定边缘三点进行圆心精定位,并利用半径阈值减小误差。实验结果表明,该方法能有效分割光纤端面图像,圆心偏差小于0.2个像素,为光纤定轴打下必要的理论基础。     

快速机扫对系统角度偏差影响分析

机扫雷达在波束扫描过程中,由于天线转动引入额外的系统角度偏差导致测角精度的下降,尤其在快速机扫时引入的系统角度偏差甚至超过测角标准差。文中基于常见的单脉冲测角,从机理上推导了机扫天线转速对系统角度偏差的影响,并提出了一种系统角度偏差补偿方法,计算机仿真结果验证了文中推导和系统角度偏差补偿方法的有效性。     

过程质量预测及判定标准的确定--统计方法在过程质量控制中的应用

为减少抽样检验所带来的风险，利用质量分布特性，提出一种新的抽样检验评估方法。     

Optimisation techniques for minimising saw teeth deflection and lumber thickness variation

Lumber size control is an essential element in maximising yield and productivity because a small reduction in rough green target size could lead to substantial savings in wood fibre. One of the key components of rough green target size is sawing variation. In this study, the optimum side clearance of band saw teeth leading to a minimum saw teeth deflection and minimum lumber thickness variation of stellite-tipped and swage-set saws when processing Triplochiton scleroxylon a tropical hardwood were examined. It was observed that the accuracy of kerf width was best with stellite-tipped saws. However, Analysis of variance (ANOVA) at 5% level of significance indicates that there was no significant difference between the accuracy of kerf width of stellite-tipped saws and swage-set saws. It also was observed that at 5% level of significance, the mean kerf width of stellite-tipped saws, which was 4.2 mm, was significantly greater than the mean kerf width of 3.06 mm of the swage-set saws. Sawing variation as indicated by standard deviation of lumber thickness was best for the swage-set saws. A quadratic relationship between sawing variation and side clearance of stellite-tipped saws was established. As the side clearance of the saw increases, the sawing variation decreases until it reaches a minimum value and thereafter, further increase in side clearance of the saw teeth results in an increase in sawing variation. It was observed that an optimum side clearance of 0.69 mm under a saw blade thickness of 1.3 mm was required to produce on the average, a minimum value of 0.42 mm for within-board standard deviation, and 0.59 mm for the total standard deviation. An error margin of less than 1% was achieved when the experimental results for the optimum side clearance was compared with a theoretical assertion.     

Hierarchically Structured Self‐Healing Sensors with Tunable Positive/Negative Piezoresistivity

It is a challenge to manufacture flexible sensors that possess easily distinguishable biomotion signals, strong response reliability, and excellent self‐healing capability. Herein, a self‐healing sensor with tunable positive/negative piezoresistivity is designed by the construction of hierarchical structure connected through supramolecular metal–ligand coordination bonds. The developed sensors can be integrated with the human body to detect multiple tiny signals, such as pronunciation, coughing, and deep breathing. Interestingly, the nanostructured elastomer sensor with and without a flexible yarn electrode shows negative and positive current signals, respectively, making it easy to be identify. Furthermore, it exhibits very fast (2 min), autonomous, and repeatable self‐healing ability with high‐healing efficiency (88.6% after the third healing process). The healed samples still possess flexibility, high sensitivity, and accurate detection capability, even after bending over 10 000 cycles. The excellent biomimetic self‐healing performance combined with the tunable piezoresistivity make it promising for next‐generation wearable electronics.